Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 250 PM EST Wed Dec 23 2020 Valid 00Z Thu Dec 24 2020 - 00Z Sat Dec 26 2020 ...Blizzard conditions expected across portions of the north-central U.S. tonight... ...Heavy snow possible for the Lower Great Lakes and eastern sections of the Ohio Valley Thursday and Friday... ...Heavy rain, damaging wind gusts, and potentially severe thunderstorms to impact much of the East on Christmas Eve and Christmas Day... A powerful surface low pressure system is currently moving across the Upper Midwest today toward the Upper Great Lakes, spreading snow and high winds to the north-central U.S. on its backside. Snowfall amounts of over 6 inches are possible across northern portions of Wisconsin and the Upper Peninsula of Michigan, as well as eastern Minnesota tonight. Heavy snow will then continue for the U.P. of Michigan and western Lower Michigan on Thursday in favored lake effect areas. Additionally, high winds are likely tonight given the depth of the surface low. High Wind Warnings and Wind Advisories are in effect for much of the Plains and into parts of the Mississippi Valley region. In the eastern Dakotas, northeastern Nebraska, much of central and southwest Minnesota, as well as northwestern Iowa, Blizzard Warnings are in place for tonight where the snow and winds could combine to create blizzard conditions, with lowering visibility and treacherous travel likely. The heavy snow threat will shift into the Lower Great Lakes and eastern Ohio Valley region by late Christmas Eve as the storm system dashes east. Total snowfall accumulations of 4 to 8 inches will be possible from central West Virginia to the southeastern shores of Lake Erie. These amounts will make travel difficult at times between Thursday evening and Christmas morning. Meanwhile, a strong cold front associated with the aforementioned low will sweep across the Ohio and Tennessee valleys tonight and into the eastern U.S. by Thursday night. Plentiful moisture from the Gulf of Mexico is forecast to stream in ahead of the cold front, leading to increasing rain chances and the possibility for isolated flooding/flash flooding for the Lower Mississippi Valley into the Tennessee Valley tonight. Also, there is a Slight Risk of severe weather in place from the Storm Prediction Center for the central Gulf Coast, where instability will be the highest and could cause strong thunderstorms tonight. Then, as the front tracks eastward Thursday, heavy rain of 1 to 3 inches is forecast for the eastern third of the country through Christmas night. Severe thunderstorms are once again possible Thursday, with an Enhanced Risk of severe weather centered over eastern North Carolina. Damaging winds and isolated tornadoes are possible. However, the potentially most widespread hazard will likely be flooding and flash flooding. A Moderate Risk of excessive rainfall is in place for northeast Pennsylvania, with a Slight Risk surrounding the Appalachians, northern Mid-Atlantic region, and Northeast. For many areas, the rain is expected to fall on top of a deep and relatively fresh snowpack from the nor'easter last week, exacerbating flooding concerns as rain could cause rapid snowmelt. Another concern is the added weight that rain could put on top of snow covered roofs, particularly across regions that still have over a foot of snow on top of buildings from north-central Pennsylvania to Vermont. Winds also remain a threat with this low pressure system as it tracks toward the East Coast. High Wind Watches have been posted for coastal New Jersey to southern Maine. The strong cold front will be a dividing line between temperatures 10 to 20 degrees below normal behind the front in the western and central U.S., with much above normal temperatures ahead of it in the Ohio Valley and Great Lakes region this evening and eventually across the East Thursday. The warm temperatures (and dewpoints) in the Northeast Thursday should be another contributing factor to flooding there, since it could cause rapid snowmelt into nearby rivers and streams. Temperatures on Christmas morning will struggle to dip below the mid-40s across New England, potentially setting daily records. The cold temperatures behind the front will support rapid freezing of any standing liquid. Elsewhere, fire danger is a concern across portions of Southern California this evening and Thursday, where the Storm Prediction Center has outlined a Critical Risk. Red Flag Warnings are in effect as well. Dry conditions and gusty winds could also cause elevated risks of fire weather in the Southern Plains. Snell/Tate Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php